VMS Help RTL Routines, MTH$, MTH$CCOS, Returns  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    OpenVMS usage:complex_number
    type:         F_floating complex
    access:       write only
    mechanism:    by value

    The complex cosine of the complex input number. MTH$CCOS returns
    an F-floating complex number.